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United States

Environmental Protection

Agency

Issue Paper

The presence and distribution of undesirable quantities of bioavailable nitrogenous compounds in the

environment are issues of long-standing concern. Importantly for us today, deleterious effects

associated with high levels of nitrogen in the ecosystem are becoming everyday news events. Excess

nitrogen in the environment is associated with many large-scale environmental concerns, including

eutrophication of surface waters, toxic algae blooms, hypoxia, acid rain, and global warming.

Unfortunately, releases of nitrogen associated with anthropogenic activities are expected to rise

throughout the foreseeable future. Whereas our current technologies for managing nitrogen in the

environment are stressed, it is reasonable to project that they are likely to fail under the increased loads

of nitrogen that are projected for the future. The potential scale of the undesirable consequences are

such that it is prudent for us to consider reasonable management and research responses now. This

Issue Paper describes a proposed three-part research and management program that is a measured

response to concerns about nitrogen pollution, particularly in the eastern United States. The program

describes: 1) steps to be taken with regard to landscape management that will improve our knowledge

of nitrogen release and management as it relates to land use; 2) investigations needed that will improve

our understanding of the factors that prevent full implementation of nitrogen management technology

in the high use landscapes that comprise 35.2% of the land cover in the eastern United States; and,

3) research that is needed to help uncover cause-and-effect relationships among trophic levels that will

provide new tools for managing nitrogen, especially on low use landscapes that comprise 64.8% of the

land cover in the eastern United States.

For further information contact Eric Jorgensen (580) 436-8545 at the Subsurface Protection and

Remediation Division of the National Risk Management Research Laboratory, Office of Research and

Development, U.S. Environmental Protection Agency, Ada, Oklahoma.

Nitrogen is added to ecosystems in enormous quantities through anthropogenic activities (Smil, 1990;

Vitousek et al., 1997). Further, these additions have been increasing; a trend that is projected to

continue (Brimblecombe and Stedman, 1982; Galloway et al., 1994; U.S. EPA, 1995; Vitousek et al.,

1997). Because nitrogen is frequently a limiting nutrient for plants and animals, increased quantities

of nitrogen in the ecosystem alters competitive relationships among terrestrial and aquatic organisms.

This phenomenon is usually manifested as eutrophication, but acidification of forested watersheds and

nitrate pollution to ground water are also symptomatic (e.g., Baker ,1992; Likens, 1992; Wedin and

Tilman, 1996; Asner et al., 1997). Excess nitrogen is not tightly retained by ecosystems but is highly

mobile (e.g., Vitousek et al., 1997) and it occurs in ecosystems under a variety of guises (i.e., nitrogen

species; NO3

, NH4, NO2, DON, TN, etc.), each of which varies in its mobility and potential for use by

organisms and expression in site biogeochemistry. Therefore, concern about nitrogen management

in ecosystems is focused not only on the amount of nitrogen present but also its transport and cycling.

Nitrogen, particularly nitrate, easily moves from terrestrial ecosystems into surface and ground waters,

including lakes, streams, rivers, and estuaries (e.g., Kahl et al., 1993; Peterjohn et al., 1996). As

nitrogen concentrates in surface and ground water sinks, increasingly frequent observations of

undesirable effects associated with eutrophication, algae blooms, hypoxia, and toxicity are observed

(Kelly et al., 1990; Likens,1992; Glibert and Terlizzi, 1999). Today, acid rain phenomena in North

America are largely associated with excess nitrogen (Aber et al., 1989; Gilliam et al., 1996). Finally,

nitrogen affects plant growth, and therefore interacts with atmospheric CO2

 (Shaver et al., 2000).

Wedin and Tilman (1996) have suggested that increasing amounts of nitrogen in the environment may

be associated with global warming and climate change (see also Vitousek et al., 1997; Shaver et al.,

2000).

Number 2:

Opportunities in Nitrogen Management Research:

Improving Applications for Proven Technologies and

Identifying New Tools for Managing Nitrogen Flux and

Input in Ecosystems

Eric E. Jorgensen

Advances in Restoration Science
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While the aforedescribed risks associated with anthropogenic

nitrogen are recognized, management options for containing and

mitigating them are poorly developed. In order to weigh risks and

assess management options, it is important that a thorough

understanding of the interactions and transport of nitrogen in

terrestrial and aquatic ecosystems and the atmosphere be

developed. The scope and magnitude of the nitrogen problem is

such that there are many research needs and many opportunities

for management intervention. It appears that a three-part nitrogen

risk management research program, integrating basic and applied

research, will contribute substantially to development of a multiscale management approach that will maximize nitrogen retention

and sequestration in terrestrial and managed landscapes, thereby

reducing loadings to aquatic ecosystems.

The description of the research program that follows results from

an expectation that the ability of terrestrial and freshwater aquatic

ecosystems to optimally retain, sequester, and transform nitrogen

can be manipulated, indeed enhanced, through application of

appropriate management technologies. This research program

would seek to identify those technologies, and identify opportunities

for application of existing techniques. This view, that management

of nitrogen will be accomplished through management of terrestrial

and freshwater aquatic ecosystems, necessarily neglects the

impact of direct atmospheric deposition. This particular source of

nitrogen input must be managed at the point of production or (as

described herein) after it is deposited in terrestrial or aquatic

ecosystems. Terrestrial and freshwater ecosystems represent

important points in the nitrogen cycle that are amenable to

management, and that, if successful when managed together, can

produce measurable benefits to water quality and aquatic resources

in both freshwater and estuarine ecosystems.

Research Program

While it is possible to conduct research on a problem as pervasive

and interrelated with biotic interactions as nitrogen in many

subject areas, in many landscapes, and over multiple spatial and

temporal scales, it appears that there is good potential to provide

measurable changes to the flux and input of nitrogen through and

into the environment, particularly in aquatic ecosystems, through

a research program that conducts applied and basic research in

three areas.

Area 1 – Landscape Management

GIS technology is rapidly reaching a level of sophistication sufficient

to characterize watershed and landscape physical, biological,

and chemical parameters. Where it is possible to characterize it

is also possible to plan and manage. This proposed research area

would seek to develop landscape management techniques and

recommendations to guide planners’ decisions regarding

appropriate zoning, development, and land use. The research

would characterize and model physical and remotely sensed

properties of landscapes and watersheds, and associate these

properties with concentrations of nitrogen ions in terrestrial and

aquatic ecosystems. These characterizations and models would

allow planners to identify potential landscapes and watersheds at

risk from eutrophication and acidification to facilitate proactive

land use planning. The characterizations and models would allow

identification of landscapes and watersheds that are potentially

highly perturbed by excess nitrogen, thereby facilitating efficient

targeting of restoration and management actions. The

characterizations and models would allow identification of

landscape and watershed attributes that are highly correlated with

risk from excess nitrogen, thereby providing clear guidance for

prescription of specific restoration and management techniques

and suggesting research themes for investigating methodologies

of maximizing and optimizing landscape and watershed retention,

sequestration, and transformation capability for nitrogen (e.g.,

Magill et al., 1996; Mander et al., 2000).

The following research tasks need to be addressed in this area:

Task 1.1 Characterize and Model the Relations of Watershed

and Upstream Land Uses and Physical and Biological

Properties to the Concentration and Load of Targeted Nitrogen

Ions in Terrestrial and Aquatic Ecosystems – Including

Estuaries, Lakes, Rivers, Streams, Ground Water, and

Sediment.

Water that is present in or entering the lakes, rivers, streams,

and ground water of a watershed is the product of a large

spatial and temporal scale integration that reflects the types

and distribution of land uses at large in the watershed and the

physical, and biological interactions occurring therein.

Task 1.2 Associate Characterizations and Models of Nitrogen

Ion Concentrations and Loads in Watersheds from Task 1.1

with Known and Predicted Exposure Risk Levels for Biota

and Health to Identify Watersheds and Landscapes that are

Currently Adversely Affected by Excess Nitrogen and Those

that are at Risk Attributable to Increasing Amounts of Nitrogen.

Where an important goal of risk management is to predict and

prevent future problems and to mitigate effects in already

heavily impacted watersheds, an important priority is to

develop and refine models that work in currently heavily

impacted watersheds and those soon to be at risk from further

nitrogen deposition.

Task 1.3 Identify Watershed and Landscape Land Use and

Physical and Biological Parameters that are Highly Correlated

with Nitrogen Ion Concentrations and Loads in Terrestrial and

Aquatic Ecosystems.

Where reduction of adverse effects can be most rapidly

achieved when cause and effect are known and consequences

are certain, identification of non-optimum land use practices

that may heavily impact at-risk watersheds is a priority.

Task 1.4 Prescribe Watershed and Landscape Specific

Restoration and Management Actions, Regarding

Manipulation of Parameters Identified in Task 1.3, to Contain

and/or Reduce Risks Associated with Excess Nitrogen

Concentration and Loading.

The nature of the nitrogen problem is such that prevention at

the source is frequently not an economically or socially

desirable option; therefore, containment of the effects of

nitrogen release is desirable through implementation of

appropriate risk reduction technologies remote from the point

of release.

Task 1.5 Identify and Prioritize Research Questions and Tasks

Indicated by the Results of Task 1.3 that Hold Substantial

Probability of Providing Measurable Refinements and

Improvements to the Techniques Prescribed by Task 1.4.

Through adaptive management, apply the skills developed

through an increasing level of management activity and

research to finding new and more effective and efficient

means for managing excess nitrogen in watersheds.

Advances in this research area will provide managers and planners

with coarse-scale correlative-tools that have a substantial

probability of providing measurable reductions to the rate of flux

and amount of nitrogen leaching to surface and ground waters,

and estuaries. These coarse-scale tools can reasonably be

expected to provide immediate management benefits. However,

the ultimate ability of management actions prescribed based upon

correlative tools to produce a large widespread benefit is unclear.

The ability of prescribed management actions can certainly be
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improved and optimized through phased implementation of

improvements to correlative tools that are based upon cause-andeffect knowledge of the system.

Area 2 – Management of High Use Landscapes

Problems associated with excess nitrogen have been recognized

for decades and are frequently associated with increasing land

use intensity and economic activity (i.e., urbanization and row

cropping). These problems include, but are not limited to, economic

loss attributable to excess fertilization, septic field failure, acid

rain, eutrophication of aquatic ecosystems, and pollution from

municipal sewage outfalls. Cover of high use lands increased

34.3% between 1982 and 1997 in the eastern United States from

60.4 to 81.1 million acres whereas cover of cropped lands

decreased 9.9% during the same period ( USDA, 2000). Together,

developed and cropped lands accounted for 35.2% of the land

cover in the eastern United States in 1997 (USDA, 2000). Impacts

to watersheds of nitrogen from these high use lands are well

known and must be accounted for. Because problems have been

associated with nitrogen for many years, numerous techniques

have been developed to minimize, or in some cases eliminate,

nitrogen leaching from high use lands to the environment.

Prescription and regulation of nitrogen management techniques

is not centralized, but falls within the authority of numerous

federal, state, and local agencies and governments. Frequently,

application of known techniques at any given local site occurs as

a matter of opportunity when willing landowners interact with

knowledgeable managers and planners. This loosely organized

system leaves significant opportunity for the identification of high

use watersheds and landscapes where application of known

nitrogen management techniques is under-utilized.

The following research tasks need to be addressed in this area:

Task 2.1 Inventory and Organize in a Central Database All

Known Sources of Nitrogen that are Associated with High

Use Landscapes, including Urbanized, Agricultural, Industrial,

and Recreational Areas. Concurrently, Inventory and Organize

in a Central Database Management Methods and

Measurements of Effectiveness for Nitrogen Management in

these Landscapes.

Historically, it has only been poorly recognized that land use

practices and nitrogen release are related; therefore,

knowledge of land uses and expected contributions to the

nitrogen problem is excessively dispersed, in the literature,

among professionals, and among management agencies.

There appears to be an opportunity to achieve significant

economy of scale improvements for the organization of

nitrogen data and information.

Task 2.2 Inventory and Model Relationships Among Physical,

Biological, Social, Economic, and Demographic Parameters

on a Watershed Specific Basis, to the Distribution of Known

Sources of Nitrogen (Task 2.1) in Conjunction with the

Distribution of the Application of Management Methods

(Task 2.2).

Management of nitrogen falls to no single entity or agency.

Therefore, many opportunities exist for the application of

state-of-the-art management interventions where currently

inadequate or absent interventions are accepted.

Task 2.3 Rank, Prioritize, and Identify Watersheds Along a

Gradient of Discordance Between the Distribution of Sources

of Nitrogen and the Distribution of the Application of

Management Methods Determined in Task 2.2.

With the strong intent to improve the situation, we should

identify watersheds that are substantive contributors to the

nitrogen problem where even current management

technologies are not being used.

Task 2.4 Provide Watershed Specific Recommendations in High

Priority Watersheds Identified in Task 2.3 to Local Managers

and Planners - in Ecological, Engineering, Environmental,

Economic, and Social Sciences – for Application of Known

Nitrogen Management Methods for High Use Landscapes.

It is reasonable to expect that local economic and social

factors may be correlated with utilization of current nitrogen

management technologies. These factors should be identified

so that programs can be developed to help local stakeholders

improve their environment and contribute to national and or

regional nitrogen management goals.

Advances in this research area will help to relieve adverse impacts

to watersheds in high use landscapes while concurrently

contributing to measurable downstream improvements of water

quality and habitat for aquatic biota in receiving waters, particularly

estuaries. Because nitrogen management techniques already

exist for many anthropogenic sources of nitrogen in high use

landscapes, measurable reductions to the rate of flux and amount

of nitrogen leaching to surface and ground water in these

landscapes should be able to be realized through identification of

under-utilized targets for technique application.

Area 3 – Management Techniques for Low Use Landscapes

Despite the recognition that excess nitrogen in the environment

has notable undesirable properties, and despite decades of

research and management practice aimed at minimizing and

eliminating nitrogen leaching from its point of production or release,

we currently face a substantial and apparently growing problem

related to excess nitrogen. One explanation for this is that

ecosystems are slowly losing their ability to optimally retain,

sequester, and transform nitrogen. Thus, nitrogen is more readily

leaching to surface and ground waters, and estuaries. By a large

majority, most of the land where the ability of the ecosystem to

process nitrogen may be degraded occurs in low use landscapes,

including parklands, wilderness, grazing lands, and forests.

Together, these land uses accounted for 68.8% of the land cover

in the eastern United States during 1997 (USDA, 2000).

The ability of these lands to retain and sequester nitrogen is not

well understood, although it is clear that increasing the amount of

nitrogen input to these landscapes frequently leads to a decreasing

ability of these landscapes to optimally retain, sequester, and

transform nitrogen. Thus, the more nitrogen that is added, the less

is retained.

This being the case, it is clear that our ability to reduce uncertainty

regarding nitrogen management results attainable from Research

Areas 1 and 2 can be greatly enhanced through an improved

understanding of the contribution of low use landscapes to nitrogen

management. Further, there is every reason to expect that

management techniques and prescriptions can be developed for

low use landscapes that will maximize and enhance their ability to

retain, sequester, and transform nitrogen, especially nitrogen

inputs attributable to atmospheric deposition.

The following research tasks need to be addressed in this area:

Task 3.1 Measure the Ability of Landscapes and Vegetative

Communities from Multiple Ecological Settings, and their

Associated Consumer, Decomposer, and Microbial

Communities, to Retain, Sequester, and Transform Nitrogen,

and Measure their Retention, Sequestration, and

Transformation Responses to Increased Levels of Nitrogen

Flux and Input.
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Measures of the basic ability of ecosystems to assimilate and

process nitrogen, and their ability to respond and adapt to

greater levels of nitrogen input are notably lacking but certainly

needed.

Task 3.2 Measure the Interaction of Landscapes and Vegetative

Communities with Producer, Consumer, Decomposer, and

Microbial Activity Relative to the Ability of Landscapes and

Vegetative Communities to Retain, Sequester, and Transform

Nitrogen.

An ability to understand and manipulate nitrogen cycling

through the ecosystem, at the level of cause-and-effect

relationships, would provide powerful tools for predicting

watershed susceptibility to increased amounts of nitrogen

and more importantly, for development of new nitrogen

management tools for a wide variety of landscapes under

many types of land use.

Task 3.3 Provide Management Recommendations for

Landscapes and Vegetative Communities Resulting from

Tasks 3.1 and 3.2, for Manipulating Sites to Optimize and

Maintain Nitrogen Retention, Sequestration, and

Transformation.

With an improved understanding of the cause-and-effect

relationships underlying nitrogen cycling, it would be possible

to tailor management interventions that will be optimum in

specific watersheds in association with specific land uses.

Task 3.4 Obtain Metrics for Projecting with Confidence how Site

Succession will Affect Nitrogen Retention, Sequestration,

and Transformation Characteristics and Identify Indicator

and Monitoring Criteria that can Predict Site Senescence.

Ecosystems change with time. Where it is desirable to predict

future conditions, the ability to predict and therefore manage

nitrogen in ecosystems must account for succession in

ecological communities.

Task 3.5 Develop Techniques and Methods for Manipulating

Producer, Consumer, Decomposer, and Microbial Individuals,

Populations, and Communities to Manage for Maintained

Native Biodiversity on Landscapes and Watersheds to

Concurrently Maximize Nitrogen Retention, Sequestration,

and Transformation Characteristics.

It is desirable that we integrate nitrogen management with

interrelated environmental concerns, most particularly native

species management, in an effort to increase management

effectiveness and benefit.

Advances in this research area, while of a basic scientific nature,

hold the promise of allowing spatially extensive low use landscapes

to maintain and improve their ability to retain, sequester, and

transform nitrogen. In this regard, they can serve as nitrogen sinks

– offsetting to some extent the degraded ability of even the bestmanaged high use landscapes to use nitrogen. Just as the

manipulation of plants, regarding their ability to produce food, has

provided the foundation for the green revolution, so is it reasonable

to expect that analogous manipulations of plants and other biota

– including individuals, populations, and communities –can produce

desirable outcomes for nitrogen management.

Conclusion

The research program for nitrogen management described herein

constitutes a reasonable – measured response – to an

environmental problem that is just beginning to be fully understood.

A program of combined applied and basic research in the Ecological,

Engineering, Environmental, Economic, and Social Sciences is

described that will identify landscapes and watersheds at risk from

excess nitrogen and prescribe management responses in both

high and low use landscapes. The program will indicate fruitful

directions for future research, leading to the development of

techniques and methods for manipulating producers, consumers,

decomposers, and microbial communities for the purpose of

maximizing and optimizing landscape and watershed nitrogen

retention, sequestration, and transformation ability.

Notice

The U.S. Environmental Protection Agency through its Office of

Research and Development funded and managed the preparation

of this Issue Paper. It has been subjected to the Agency’s peer

and administrative review and has been approved for publication

as an EPA document.

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United States

Environmental Protection

Agency

EPA/600/S-02/003

June 2002

National Risk Management

 Research Laboratory

Cincinnati, OH 45268

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